Sermo operates the leading online professional network for physicians in the United States. Doctors use Sermo free of charge to post surveys regarding diagnostic and treatment concerns and to discuss these concerns, as well as challenges with managing their practices. Sermo earns revenue by charging clients who would value early information regarding the effectiveness of new drugs and medical devices-investment managers, pharmaceutical companies, and regulatory authorities. Clients cannot participate in doctors' online discussions, but they can view survey results and post their own surveys to Sermo's physician members. The case discusses challenges confronting Sermo in mobilizing this two-sided platform and in balancing the sometimes conflicting needs of the platform's two sides.